1. Field of the Invention
The present invention relates to a three-dimensional shape measuring apparatus, and more particularly to a non-contact and fast three-dimensional shape measuring apparatus.
2. Description of the prior Art
In the past, various methods have been used to non-contact measure a three-dimensional shape. They include an interference measuring method which uses a coherent light, and a method of reading a light sectional image with slit light. The interference measuring method has an advantage in that all surfaces of an object can be simultaneously measured with a high precision but a disadvantage in that the measurement of the shape is difficult to attain when an irregularity on the surface of the object is much larger than a light wavelength. In the light sectional image reading method, it is difficult to measure an irregular shape of an order of the light wavelength and hence a high precision measurement is not attained. In order to resolve the above disadvantages, a three dimensional shape measuring method has been proposed in which an in-focus state detection optical system having an internal light source is mounted on a carriage which is moved such that the optical system is focused to an surface of an object. (Japanese Patent Publication No. 40231/1971). In this method, the shape is measured with a high precision irrespective of the irregularity on the surface of the object. However, in the prior art method, a large quantity of energy is required to move the carriage which carries the in-focus state detection optical system because of the large weight of the movable portion.
When a fine irregularity is included on the surface of the object, more exact information is obtained by expressing the irregular shape by height or distance as well as an inclination angle than by expressing it only by the distance. In the prior art methods, exact information cannot be obtained by this method.